Yoichi Ose

Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

A pulsed gas electron diffraction apparatus was developed and applied to investigate an alignment process of molecules in intense laser fields. A two-dimensional (2D) electron diffraction pattern of jet-cooled CS2 in intense nanosecond laser fields (1064 nm, ∼0.64 TW/cm2, 10 ns) was measured using short-pulsed 25 keV electron beam packets (∼7 ns) generated by irradiating a tantalum photocathode with the 4th harmonics of pulsed YAG laser light. The observed anisotropic 2D diffraction pattern was analyzed quantitatively by taking into account the spatio-temporal distributions of the laser pulses, the electron beam packets, and the molecular beam through a numerical simulation of the observed diffraction pattern. The anisotropy of the spatial distribution of molecular axes of CS2 in the laser polarization direction is accounted for by the effect of the intense laser fields. Considering the spatio-temporal averaging effect, the temporal pulse width of an electron packet required for real-time probing of the a...

Direct Observation of Field Emission Sites in a Single Multiwalled Carbon Nanotube by Lorenz Microscopy

Emission sites were observed as bright spots near the tip end of a multiwalled carbon nanotube (MWNT) by means of Lorenz microscopy. The bright spots appeared above electric fields as electrons were emitted. A marked fluctuation was observed in the emission current above 20–30 µA, which was closely related to structural changes at the tip of the MWNT. The layers of the MWNT were peeled off during field emission and they functioned as the second emission sites for the concentration of electric field.

In situ observation of field emissions from an individual carbon nanotube by Lorenz microscopy

In situ observation of field emissions from an individual carbon nanotube (CNT) was performed by Lorenz microscopy. A bright spot appeared by Lorenz microscopy at the end of the CNT tip during field emission. The bright spot is assumed to be related to the emission site on the CNT. A drastic fluctuation was observed in the emission current above a few tens of microamperes, which was closely related to structural changes at the tip of the CNT. The layers of the CNT were peeled off and they worked as a second emission site by concentration of the electric field.

Improved CD-SEM optics with retarding and boosting electric fields

Because of rapidly decreasing line-width of integrated circuits, it is necessary to measure and control their critical dimensions with high accuracy. Hitachi has developed a new critical-dimension-measurement scanning electron microscope S-9000 series, which has a new electron optics with retarding and boosting electric fields. The upper pole piece of the objective lens is kept at a high positive voltage with respect to the ground so as to reduce aberration of the objective lens drastically. To optimize the boosting voltage we have developed optics simulators that is capable of computing aberration coefficients in electric and magnetic mixed fields. At the optimized boosting voltage of around 5kV, 3nm resolution is achieved for a final accelerating voltage of 800V. The high boosting voltage is effective in imaging bottoms of contact holes having high aspect ratios.

Electrostatic ion guide using double cylindrical electrode for atmospheric pressure ionization mass spectrometry

A novel electrostatic ion focusing lens that consists of two cylindrical electrodes positioned coaxially with each other is described. Square openings are formed in the inner electrode and their angular positions alternate by 90° with respect to the neighboring openings in the axial direction. When a potential difference is applied between the inner and outer electrodes, an electric field penetrates into the interior of the inner electrode through the openings. In the capillary electrophoresis/mass spectrometry analysis of peptides, use of the lens makes it possible to apply a higher voltage to the postacceleration dynode and the signal to background ratio is improved by a factor of 7.

Correction method for high-precision CD measurements on electrostatically charged wafers

A correction method for automatic, high-precision CD-measurements on electrostatically charged wafers has been developed and installed in the Hitachi CD-SEM S-9260 to evaluate its performance. There are two types of charging: global and local. Global charging is stable and spreads all over a wafer while the local charging area is limited within the beam scanning area. A conventional CD-SEM has two weak points with respect to those charged wafers: one is failure at the positioning and autofocusing procedure which interferes with the fully automatic measurement sequence, and the other is disturbance of optical magnification which degrades the precision of CD-measurement values. By probing the global charging voltage with an electrostatic voltmeter prior to the CD-measurements, we subtract the voltage from a retarding voltage and then apply it to the wafer holder. The beam-focusing condition can stay within the fully automatically tunable range. And by generating numerical functions to represent the relationship between the global charging voltage, wafer height, excitation current of the objective lens and optical magnification, with the help of electron optical simulations, we can calculate the true optical magnification and the correct CD-measurement values. The local charging voltage is derived from the voltage shift of S-curves of secondary electron yield between conductive and insulated wafers measured with an energy filter. We correct the CD-measurement values using the simulated proportional relationship between magnifications of the electrostatic micro-lens and the local charging voltage. The coefficient is almost constant when the charging area is smaller than an equivalent circle of 100mm radius. We demonstrate that the CD-measurement values are successfully corrected within 0.1 percent in deviation for both charging types.

Three-dimensional analysis of ion beam deflection by the magnetic field at H− ion sources for the negative-ion-based neutral beam injection

In negative-ion-based neutral beam injection (NBI) systems for the large helical device (LHD), beams must be transported over 13 m from the H− ion source to the injection port. In order to clarify beam deflection by the electron deflection magnets set in a beam extraction grid (EG) and to control beam transport direction, we analyzed beam trajectories. The physics of the beam deflection was studied with theoretical calculations and the deflection angle was estimated by 3D beam trajectory simulation. The evaluated deflection angle was 10 mrad in the opposite direction of the electron deflection when the maximum magnetic field on the beam axis was 480 G and the beam energy was 83.2 keV. The electrostatic lens effect on the beam deflection at the EG exit was estimated to be larger than the magnetic field effect. This deflection was reduced to 2 mrad by a 1.3 mm displacement of the grounded grid (GG) aperture, a result in agreement with experimental results of a 1/3-scale model for the LHD ion source. The max...

3D electron optics simulation method for cathode ray tubes

A numerical simulation method for 3D electron optics in an electromagnetic field is described. The method features the following: (1) electric field analysis by a boundary-fitted coordinate transformation method in conjunction with a domain decomposition and overlapping technique; (2) consideration of the space-charge effect due to the electron beam in a self-consistent electric field; (3) magnetic field analysis based on a current sheet and a boundary-element method; and (4) interactive geometric modeling and numerical grid generation based on the same method used for electric field analysis. The method has been applied to electron optics simulation for the electron gun of a cathode-ray tube with a typical deflection yoke. A comparison between computed and measured screen spot profiles verifies the method and demonstrates its capabilities. >

High resolution CD-SEM system

Because of rapidly decreasing line-width of integrated circuits, it is necessary to measure and control their critical dimensions with high accuracy. We have developed a new critical-dimension-measurement scanning electron microscope (CD-SEM) S-9000 series, which has a new electron optics with retarding and boosting electric fields. To optimize the boosting voltage we have developed optics simulators that are capable of computing aberration coefficients and secondary electron detection efficieny in electric and magnetic mixed fields. At the optimized boosting voltage of around 5 kV for a final accelerating voltage of 800 V, not only 3 nm resolution but also highlighted bottom imaging of high aspect ratio contact holes is obtained.